package dataStructure.chapter03_链表.part1单链表.java3;

/**
 * @author https://gitee.com/W_Jun
 * @date 2022-01-16 19:57
 * @Description 增加一个虚拟头结点。
 *              构造方法和node()方法要进行调整，以及涉及到index=0的方法需要调整。
 */
public class MyLinkedList<E> extends MyAbstractList<E> {

    private Node<E> first;

    public MyLinkedList() {
        first = new Node<>(null, null);
    }

    private static class Node<E> {
        E element;
        Node<E> next;

        public Node(E element, Node<E> next) {
            this.element = element;
            this.next = next;
        }
    }

    @Override
    public void clear() {
        size = 0;
        first = null;
    }

    @Override
    public E get(int index) {
        return node(index).element;
    }

    @Override
    public E set(int index, E element) {
        Node<E> node = node(index);
        E old = node.element;
        node.element = element;
        return old;
    }

    @Override
    public void add(int index, E element) {
        rangeCheckForAdd(index);
        Node<E> prev = index == 0 ? first : node(index - 1);
        prev.next = new Node<>(element, prev.next);
        size++;
    }

    @Override
    public E remove(int index) {
        rangeCheck(index);
        Node<E> prev =index == 0 ? first : node(index - 1);
        Node<E> node = prev.next;
        prev.next = node.next;
        size--;
        return node.element;
    }

    @Override
    public int indexOf(E element) {
        if (element == null) {
            Node<E> node = first;
            for (int i = 0; i < size; i++) {
                if (node.element == null) return i;
                node = node.next;
            }
        } else {
            Node<E> node = first;
            for (int i = 0; i < size; i++) {
                if (element.equals(node.element)) return i;
                node = node.next;
            }
        }
        return -1;
    }

    /**
     * 获取index位置的节点。add(int index, E element)、get(int index)、set(int index,E element)用到。
     */
    private Node<E> node(int index) {
        rangeCheck(index);
        Node<E> node = first.next;//有了虚拟头结点，就需要从first.next开始获取
        for (int i = 0; i < index; i++) {
            node = node.next;
        }
        return node;
    }

    @Override
    public String toString() {
        StringBuilder string = new StringBuilder();
        string.append("size=").append(size).append(", [");
        MyLinkedList.Node<E> node = first.next;//有虚拟头结点，从first.next开始
        for (int i = 0; i < size; i++) {
            if (i != 0) {
                string.append(", ");
            }
            string.append(node.element);
            node = node.next;
        }
        string.append("]");
        return string.toString();
    }

}
